Stripping or re-painting, or just painting over depends most (first!) on what you want the final product to look like, then (second) on what the current paint is doing.
For example, you want a “perfect” varnish/hand-rubbed (stained) finish showing off the “raw wood” with its beuty. (Like an old cabinet or bookcase. Then, well yes, you need to strip off the old paint (all of the old paint!) then begin with the new stain, the new polyurethane (replaces varnish). ANd you would proably want three-four coats of the polyurethane, each spread on very thin and uniform.
OK, now assume you want a interior grade (bedroom or workroom) solid paint covering. The old paint is in good technical condition (not peeling or mildewy or torn up. It just dirty and the wrong color. Or rubbed through in a few spots so it looks ugly. In that case, clean it with a household cleaner (Windex-409-or whatever), rub & rinse thoroughly but quickly to get the dirt and soap film off, let it dry well, and just repaint. (You don’t want to paint over the wet surface.)
Stripping is needed only when you must remove all of the old the paint from all of the surface.
Sanding works on the surface of the old paint (wearing it off), then on the wood below the surface when the paint is rubbed through. So think of it only as best and simplest and safeest on larger, flat, square-sided panels. It also works when you sand not to remove paint, but to get a smooth surface (remove irregular paint areas or rough areas) to leave a smooth flat surface ready for the next complete color. Sanding IS WORK. A iron-shaped vibrating sander with the stick-on pads is MUCH safer that the heavier rolling sanders - those things will tear up wood and gouge grooves if you are not strong enough to maintain complete control. The rollers are faster though.
Stripping is not harder than sanding (certainly messier) and must be respected, but not feared. Sanding will get a lot a dust that you need to expect to vacuum. Stripping leaves a greasy-like gunk that should be allowed to fall on a disposable surface, then wrapped up and disposed of. When I have to strip (to leave a bare surface ready to stain), I prefer to use the water-soluable chemicals that are “sticky” for verticals and flats.
Safety? If you get the stripper on you, and you wash it off quickly, you might get a sun-burn like irriatation. Leave it on for a while? Yes, you will get burned. Always use your heavy gloves that go up to near your elbows, and remove them like a surgeon does (invert as you roll them off to trap the chemicals in the rolled up glove.
Stripping required only if you to remove the old paint completely, and don’t have access to a nice flat even smooth surface for a square pad sander or a iron-shape flat bottom sander. (Trim, curlicues, curved moldings, and carvings? Yes - They’ll need stripping.)
good info, robt, thnanks!